In applications of current digital cameras and video cameras, automatic recognition of a photographed subject, especially a human face, and photographing in an automatic focusing manner have been used widely. A human face detection technology is used to locate an accurate position of a human face in a viewfinder frame, and then automatically use the human face as a photographed subject for performing focus detection and performing metering, so as to set an accurate focus and an accurate exposure. However, existing face detection technologies do not take a variation relationship between a human face size and a focal length into consideration, and do not take a variation relationship between the human face size, a photographing distance, a focus, and the focal length into overall consideration either. Consequently, in a photographed picture, the size and a position of the human face cannot be automatically adjusted, and a photographer still needs to shift a position of a camera or a video camera and perform manual focusing to implement the adjustment.